To me it looks like the base of Q20 and the junction of the two resistors connected to it should all go to ground .

Did Wahab also want to do that and forgot to show the ground ?

Quote:

Originally Posted by donpetru

@wahab, in the last diagram you posted would be better to be connected to GND the base pin Q20 transistor. It's better that way.

I attach in the next few days own version of this amplifier with PCB. It will be a surprise.

Hi Donpetru and Ashok

You are right that connecting the said node to ground seems
at first look logical but i willfully connected it this way since
it allow to get rid of current bias running through the ground
as well as limiting the effect of parasistic capacitance.

If this point is connected to ground then there will be an AC
coupling from emitter and collector to ground through
the device parasistic capacitances.

Indeed , the resistors having same value , the potential is
close to 0V at this node.

I did some tests with and without the transistor Q20 and arrived at the following conclusions:

- If used Q20, then THD value decreases from 0.008% to 0.007% - keeping C12 = 10nF (the capacitor is not critical but after testing it's better 10nF instead of 1nF);

- If we use three pairs of MOS transistors when power dissipation of each transistor (when the amplifier operates in 4 ohms) is only 25W. Seeing this, I simulated the operation amplifier into 2 ohms and in this case each MOS transistor power dissipation is 46W. So, the amplifier can handle quite stable 2 ohm loads. One advantage that you rarely see in other amplifier diagrams.;

- In the last amplifier diagram posted by @wahab we recalculated the value of C13:
C13 = (0.04 * I) / Uz = (0.04 * 0.0025) / 3.6 = 0.27uF
I will choose a standardized value of 0.47uF (once again, value is not critical, but it's better that way);

Donpetru hardly wait to see your circuit you come up.wahab
Today I made the laser photocopy for the layout after my design. I didn't used Q20 because you just came up a few days a go with that idea.
It is worth to implement the Q20 into my layout and go to Staples for laser printing again?
I waited a few weeks and I had that idea it will be no further improvement or other mode on the circuit.
I would like to ahead with these project also.Guys do you mind if donpetru post his creation here or keep these thread for the Hitachi laterals?
I ask these because once I already ask the moderator (Tinitus) to clean up the mess in these tread... I respect those people interest (opinion) who follow these thread!!! So please vote or just let us know what do you think!
To me is OK but these thread not just about me!

Very nice Alex!! Congrat...
In did these is so nice it would be great to start a GB if it will be enough interest..
I didn't went over to look for any error. I'm just tired to do that because I made several layout with out any software.
Only one question I have
Do we need all those 100uF caps for each mosfet?

Today I made the laser photocopy for the layout after my design. I didn't used Q20 because you just came up a few days a go with that idea.
It is worth to implement the Q20 into my layout and go to Staples for laser printing again?
I waited a few weeks and I had that idea it will be no further improvement or other mode on the circuit.
I would like to ahead with these project also.

I m sorry to come late with this modification as it was consequent
to the choice of 2SA1360 instead of the expensive 2SA1407 and
after i compulsed the datasheets more closely.

2SA1360/2SC3423 have only 5W max TDP while using 65V rails will
lead to about 1.2W dissipation for Q7 , quite a lot for a single device so
i elected to use two devices with each one dissipating 0.6W.

As pointed by Donpetru this reduce THD slightly but this is not
the reason that pushed me implementing this mod , it is a question
of long term reliability as my experience is that local hot spots
on a PCB will forcibly induce failures sooner or later.